While not restricted thereto, this invention finds immediate application in simple, inexpensive power supply circuits which are especially useful for powering small loads such as logic circuits, microprocessor chips and other small D.C. powered devices.
It is known from U.S. Pat. No. 3,943,423 to Philip A. Hoffman entitled "Battery Charging Circuit" and issued on Mar. 9, 1976 to provide a battery charging circuit which eliminates the need for a relatively bulky and heavy voltage step-down transformer, and which, when recharging batteries in a hand tool or the like, needs simply to be connected to a conventional, 117 volt 60 Hz household outlet and to the battery cell or cells which are to be recharged. Other outlet voltage levels and/or supply frequencies can be used as well. The known charging circuit of the aforesaid Hoffman patent comprises a variable resistance switch preferably realized in the form of a NPN junction transistor and Darlington-connected other transistors operatively associated with a feedback circuit. This known circuit has, in addition to the transistors and resistors, two rectifying diodes and two capacitors, resulting in a circuit which, particularly because of the need for the capacitors and a considerable number of passive components, becomes relatively more expensive to realize as an integrated circuit than the present invention and would be somewhat bulky and more expensive to miniaturize than the present invention using other techniques for incorporation into cordless devices.
It is known from the further U.S. Pat. No. 3,970,912 issued on Jul. 20, 1976 to Philip A. Hoffman and entitled "Battery Charging Circuit" to provide a battery charging circuit free of transformers and operatively arranged to produce current pulses which are supplied to the battery or batteries to be recharged via the inductance of an electric motor, which forms part of a cordless hand tool or the like. This circuit, while not requiring capacitors, does require at least two diodes and an inductance, albeit the inductance of an electric motor which is a portion of a powered hand tool or the like. As a result, this circuit has somewhat limited utility because of the requirement for an inductance, and, in particular, the inductance provided by a D.C. electric motor.
A considerable number of battery chargers have been proposed and are known from the general prior art including U.S. Pat. Nos. identified as follows:
______________________________________ U.S. Pat. No. Patentees Issue Date ______________________________________ 3,281,639 Norman M. Potter October 25, 1966 3,735,233 Richard B. Ringle May 22, 1973 3,876,921 John H. Bigbee, III April 8, 1975 4,013,934 George J. Frye March 22, 1977 4,140,958 Charles R. Groeschel February 20, 1979 4,158,813 Robert W. Ellis et al. June 19, 1979 4,162,439 Arthur Schneider July 24, 1979 4,186,335 Harold J. Cahill January 29, 1980 4,220,905 William T. Quarton September 2, 1980 4,266,178 Tatsushi Asakawa May 5, 1981 4,292,578 Robert L. Steigerwald et al. September 29, 1981 4,321,523 Ronald O. Hammel March 23, 1982 4,348,619 Ray et al. September 7, 1982. ______________________________________
It is also known from Mims III "Engineer's Notebook A Handbook of Integrated Circuit Applications", First Edition, Second Printing, pg. 95, Radio Shack, A division of the Tandy Corporation, U.S.A. (1979) to use integrated circuits in battery chargers.
It is known from U.S. Pat. No. 3,049,623 to Wilber E. DuVall entitled "Auxiliary Power Supply" and issued on Aug. 14, 1962 to provide a power supply which includes a rectifier and storage capacitance, the latter being coupled to output terminals via transistor circuitry.
Voltage regulator circuits which are Zener diodes are widely used, examples can be seen in U.S. Letters Patents identified as follows:
______________________________________ U.S. Pat. No. Patentees Issue Date ______________________________________ 3,217,229 Lyttleton W. Ballard November 9, 1965 3,530,367 Robert A. Gardenghi March 7, 1969. ______________________________________